1. Field of the Invention
The present invention pertains generally to beds, and more particularly to beds for relocating a person, commonly referred to as a gurney or stretcher. The stretcher may further include a hoisting, lifting, elevating, or raising device and wheels for free traveling. Most particularly, the present invention pertains to such gurneys that are compatible for use with magnetic imaging systems such as MRI and NMR systems commonly found within a health care facility.
2. Description of the Related Art
Throughout the ages, medical practitioners were limited by what they could detect with their senses. Visual inspection of a patient might reveal a joint dislocation or exterior wounds, a sore throat indicative of a disease or infection, or even a color indicative of a condition such as jaundice. Combining information derived from other senses, such as lymph node swelling identified through tactile palpitations, could confirm the diagnosis of a disease or infection. Sounds were amplified with stethoscopes, and a practitioner might detect an unusual odor or smell, such as sweet or foul smells. While much less common, even taste was used, such as to detect a salty sweat consistent with cystic fibrosis. In spite of the centuries of refinement, these diagnostic techniques lacked the ability to give the physician access to the interior of the human body, without harming, hindering or seriously disrupting a person.
A little more than a century ago, with the discovery of x-rays and the refinement of photographic film technology, medical practitioners could for the first time noninvasively view internal body features. This drastically improved a physician's ability to accurately diagnose and treat diseases and injuries, and has become a mainstay of medical practice. While x-rays are very effective in viewing density variations, such as the shape and size of a bone fracture or a tissue mass, they do little in distinguishing the type or biological activity of the tissues.
Much more recently, Magnetic Resonance Imaging (MRI) machines, which may also be referred to as Nuclear Magnetic Resonance (NMR) or Magnetic Resonance Tomography (MRT) machines, have been developed that complement the capabilities of x-ray machines. MRI machines develop contrasting images of various soft tissues of the body. This is done without the need for harmful ionizing radiation of x-ray equipment. As a result, modern MRI machines are very common in health care facilities, and are used extensively for medical diagnostics.
As an essential part of proper operation, MRI machines create an extremely strong magnetic field. This magnetic field can undesirably turn common articles made from materials such as iron and steel into dangerous projectiles that can harm patients, medical personnel, and the machines themselves. In addition to human danger and mechanical damage, the result of an accident involving these vital diagnostic machines will often also include shutting down the machine for an extended period of time. Since these machines are typically very expensive, there is rarely excess capacity available. Even short-term shut-down of a machine can lead to costly and life-endangering delays in diagnosing and treating patients. For smaller facilities that rely upon a single machine, this can be particularly critical, since the loss of the diagnostic capability of these machines at an inopportune moment can literally lead to further loss of life. Consequently, much care must be taken to avoid bringing magnetic objects into the vicinity of the strong magnetic field.
While many magnetic objects are visually identifiable, this is not always the case. Some materials are very hard to visually distinguish. In addition, while most modern surgical implants have been designed to be non-magnetic in consideration for the common use of this diagnostic equipment, an occasional patient may unknowingly have either a very old implant or through traumatic injury have a foreign object within their body that is magnetically susceptible. These magnetic objects can cause harm to the patient and equipment, particularly where such objects are relatively large or in troublesome locations within the patient.
Even medical personnel who have been educated about the hazards of MRI machines and who are familiar with the risk of magnetic materials will sometimes forget or otherwise fail to recognize that a particular object is magnetic. In other instances, an emergency may arise and the medical personnel may not have time to consciously consider whether an item or piece of equipment needed for the emergency is magnetic.
While normally considered less dramatic and consequential than magnetic objects flying towards an MRI machine, the presence of small magnetic objects can also disrupt the proper operation of the MRI equipment. MRI machines depend not only upon very strong magnetic fields, but also upon very consistent fields. Unfortunately, even quite small magnetically susceptible materials tend to distort the field undesirably, and so can consequentially degrade the images produced.
In consideration of the foregoing, most MRI facilities are designed with limited and controlled access. This will commonly include a magnetic material detection station, such as a screening portal, through which all patients, medical and service personnel must pass. The magnetic material detection station is generally sufficiently separated from the machine to allow safe detection and correction. For example, if a building repair person unknowingly carrying a steel hammer were to pass through a screening portal, the portal would signal the presence of the hammer in time to allow the building repair person to discard the hammer. The repair person would the pass through the screening portal a second time prior to entering the MRI room to confirm that no other magnetic objects were present. In this manner, the screening portal acts as a vital safeguard and reminder.
Exemplary screening apparatus are described in the following U.S. patents and published patent applications, the teachings and contents which are incorporated herein by reference: U.S. Pat. No. 6,956,369 by Czipott et al, entitled “Screening method and apparatus”; U.S. Pat. No. 7,106,056 by Czipott et al, entitled “Security screening method and apparatus”; U.S. Pat. No. 7,154,266 by Czipott et al, entitled “Screening method and apparatus”; U.S. Pat. No. 7,239,134 by McClure et al, entitled “Screening method and apparatus”; U.S. Pat. No. 7,315,166 by Czipott et al, entitled “Magnetic resonance imaging screening method and apparatus”; U.S. Pat. No. 8,035,377 by Czipott et al, entitled “Method for excluding magnetic objects from magnetic resonance imaging facility”; 2008/0281187 by Massengill et al, entitled “Ferromagnetic threat detection method apparatus”; and U.S. Pat. No. 8,115,480 by Masubuchi et al, entitled “Magnetic body detector”.
Within most medical facilities, patients are transported upon gurneys that are fabricated from a steel framework. Many smaller components such as fasteners, casters, and auxiliary components are also commonly fabricated from steel. Steel components used in the fabrication of gurneys are generally of relatively lower cost to fabricate than other components, while providing excellent strength to weight ratios. A steel surface is quite hard and scuff and scratch resistant, and is easily cleaned and sanitized. Furthermore, the condition of steel components can often be ascertained from a simple visual inspection. Consequently, gurneys have been preferentially fabricated from steel for centuries. Unfortunately, steel is magnetic, and so is incompatible with magnetic imaging equipment.
Another common gurney material is plastic. In contrast to metals, over time and particularly when under load, plastic components tend to sag or flow. Imminent failures tend to be harder to detect. Furthermore, the plastic surfaces are softer than metal counterparts, and so are more easily scuffed or roughened. Cleaning and sanitization can be more difficult and complex, and the gurneys may require more frequent replacement.
While some satisfactory gurneys exist that are made entirely from non-metallic materials, it remains desirable to fabricate a gurney from metal components where possible, while avoiding undesirable triggering of screening portals. Since most screening portals used with MRI machines are designed to detect magnetically susceptible materials such as steel and iron, some individuals have tried to fabricate gurneys from non-magnetically susceptible materials. Aluminum, for example, is not magnetically susceptible.
Some alloys of stainless steel are also either not magnetically susceptible, or are drastically less so than steel. As a result, these materials are generally safe to use in the vicinity of MRI machinery. Some gurneys have been fabricated from stainless steel alloys. Depending upon the composition, these alloys may form austenite, which is not ferromagnetic. However, austenite is paramagnetic in nature, and so is still attracted to an externally applied magnetic field, albeit less forcefully than ferromagnetic materials such as steel, martensite alloys and ferrite.
Many MRI screening portals use electromagnetic fields to detect paramagnetic and ferromagnetic materials. These electromagnetic fields can induce electrical current in electrically conductive materials such as aluminum and stainless steel. Unfortunately, induced electrical currents in turn generate magnetic fields, which means that many screening portals cannot adequately distinguish the electrically conductive gurney materials such as austenite stainless steel and aluminum from ferromagnetic gurney materials. As a result, these prior art attempts to fabricate non-magnetic metallic gurneys have failed to gain wide acceptance due to undesirable triggering of screening portal alarms.
A variety of patents and published applications that illustrate various gurneys and patient transport systems, the teachings and contents which are incorporated herein by reference, include: U.S. Pat. No. 5,111,541 by Wagner, entitled “Non-metallic gurney for patient transport”; FR 2,789,302 by Antar; U.S. Pat. No. 6,640,364 by Josephson et al, entitled “Pedestal for use with patient transport system for multiple imaging systems”; U.S. Pat. No. 7,216,383 by Heinl et al, entitled “Support device for a patient”; U.S. Pat. No. 8,132,276 by Klemm et al, entitled “Patient support apparatus”; U.S. Pat. No. 7,490,377 by Ahlman, entitled “Patient single surface system”; U.S. Pat. No. 7,784,121 by Ahlman, entitled “Patient single surface system”; and U.S. Pat. No. 8,046,851 by Ahlman, entitled “Patient single surface system”. In addition to the foregoing patents, Webster's New Universal Unabridged Dictionary, Second Edition copyright 1983, is incorporated herein by reference in entirety for the definitions of words and terms used herein.